Visible spectra of (474640) 2004 VN112-2013 RF98 with OSIRIS at the 10.4 m GTC: evidence for binary dissociation near aphelion among the extreme trans-Neptunian objects

0.18 MB·

by  J. de León

MNRAS000,1–6(2017) Preprint11January2017 CompiledusingMNRASLATEXstylefilev3.0
Visible spectra of (474640) 2004 VN –2013 RF with OSIRIS at
112 98
the 10.4 m GTC: evidence for binary dissociation near aphelion
among the extreme trans-Neptunian objects⋆
J. de León,1,2† C. de la Fuente Marcos3 and R. de la Fuente Marcos3
1InstitutodeAstrofísicadeCanarias,C/VíaLácteas/n,E-38205LaLaguna,Tenerife,Spain
7 2DepartamentodeAstrofísica,UniversidaddeLaLaguna,E-38206LaLaguna,Tenerife,Spain
1 3UniversidadComplutensedeMadrid,CiudadUniversitaria,E-28040Madrid,Spain
0
2

n Accepted2017January4.Received2016December23;inoriginalform2016October20
a
J

0 ABSTRACT
1 The existence of significant anisotropies in the distributions of the directions of perihe-
lia and orbital poles of the known extreme trans-Neptunian objects (ETNOs) has been
]
P used to claim that trans-Plutonian planets may exist. Among the known ETNOs, the pair
(474640)2004 VN –2013 RF stands out. Their orbital poles and the directions of their
E 112 98
periheliaandtheirvelocitiesatperihelion/aphelionareseparatedbyafewdegrees,butorbital
.
h similaritydoesnotnecessarilyimplycommonphysicalorigin.Inanattempttounraveltheir
p physicalnature,visiblespectroscopyofbothtargetswasobtainedusingtheOSIRIScamera-
-
spectrographatthe10.4mGranTelescopioCanarias(GTC).Fromthespectralanalysis,we
o
r findthat474640–2013RF98 havesimilarspectralslopes(12vs.15%/0.1µm),verydifferent
t fromSedna’sbutcompatiblewiththoseof(148209)2000CR and2012VP .Thesefive
s 105 113
a ETNOsbelongtothegroupofsevenlinkedtothePlanetNinehypothesis.Adynamicalpath-
[ wayconsistentwiththesefindingsisdissociationofabinaryasteroidduringacloseencounter

withaplanetandweconfirmitsplausibilityusingN-bodysimulations.Wethusconcludethat
1
v boththedynamicalandspectroscopicpropertiesof474640–2013RF98 favourageneticlink
4 andtheircurrentorbitssuggestthatthepairwaskickedbyaperturbernearaphelion.
3
Key words: techniques: spectroscopic – techniques: photometric – astrometry – celestial
5
mechanics–minorplanets,asteroids:individual:(474640)2004VN –minorplanets,as-
2 112
0 teroids:individual:2013RF98.
.
1
0
7
1 1 INTRODUCTION the Sun at hundreds of au. This interpretation was further sup-
: portedbydelaFuenteMarcos&delaFuenteMarcos(2014)with
v The dynamical and physical properties of the extreme trans-
i aMonte Carlo-based study confirming that theobserved patterns
X NeptunianobjectsorETNOs(semimajoraxis,a,greaterthan150 inETNOorbitalparameter spacecannot resultfromselectionef-
au,andperiheliondistance,q,greaterthan30au,Trujillo&Shep-
r fectsandsuggestingthatoneormoretrans-Plutonianplanetsmay
a pard2014)areintriguinginmanyways.Theirstudycanhelpprobe
exist. A plausible multi-planet dynamical scenario was explored
theorbitaldistributionofputativeplanetsgoingaroundtheSunbe-
by de la Fuente Marcos, de la Fuente Marcos & Aarseth (2015).
tweentheorbitofPlutoandtheOortCloudaswellasunderstand
Based on observational data, and analytical and numerical work,
the formation and evolution of the Solar system as a whole. The
Batygin & Brown (2016) presented their Planet Nine hypothesis
firstETNOwasfoundin2000,(148209)2000CR ,anditsdis-
105 thatwasfurtherdevelopedbyBrown&Batygin(2016),butques-
coverywassoonrecognisedasaturningpointinthestudyofthe
tionedbyShankmanetal.(2016).TheorbitsofsevenETNOs—
outerSolarsystem(e.g.Gladmanetal.2002;Morbidelli&Levison
Sedna, 148209, (474640) 2004 VN , 2007 TG , 2010 GB ,
2004).Thecurrenttallystandsat21ETNOs. 112 422 174
2012 VP and 2013 RF — were used by Brown & Batygin
Trujillo & Sheppard (2014) were first in suggesting that the 113 98
(2016) topredict theexistenceoftheso-calledPlanetNine,most
dynamical properties of the ETNOs could be better explained if
probablyatrans-Plutoniansuper-Earthinthesub-Neptunianmass
a yet to be discovered planet of several Earth masses is orbiting
range.Outofthe21knownETNOs,onlySednahasbeenobserved
spectroscopically(seeFornasieretal.2009).
⋆ BasedonobservationsmadewiththeGTCtelescope,intheSpanishOb-
Among the known ETNOs, the pair 474640–2013 RF
servatoriodelRoquedelosMuchachosoftheInstitutodeAstrofísicadeCa- 98
narias,underDirector’sDiscretionaryTime(programIDGTC2016-055). clearly stands out (de la Fuente Marcos & de la Fuente Marcos
† E-mail:[email protected] 2016). The directions of their perihelia (those of the vector from
(cid:13)c 2017TheAuthors
2 J. deLeón, C. delaFuenteMarcos andR. delaFuenteMarcos
the Sun to the respective perihelion point) are very close (angu- to0′.′12.2Nootherdata,besidesthese38observations,itsHvalue,
larseparationof9◦.8),theirorbitalpolesareevencloser(4◦.1),and anditsorbitalsolutions,areknownaboutthisETNO.
consistentlythedirectionsoftheirvelocitiesatperihelion/aphelion Asteroid 474640 has been classified asan extreme detached
arealsoveryneareachother(9◦.5),althoughimprovedvaluesare objectbySheppard &Trujillo(2016) andtheir integrationsshow
given in Section 3.3; in addition, they have similar aphelion dis- thatitisastableETNOwithinthestandardeight-planets-onlySo-
tances, Q (589 au vs. 577 au). Assuming that the angular orbital lar system paradigm; this result is consistent with that in Brown
elementsoftheETNOsfollowuniformdistributions(i.e.theyare & Batygin (2016). In Sheppard & Trujillo (2016), 2013 RF is
98
unperturbedasteroidsmovinginKeplerianorbitsaroundtheSun), classifiedasanextremescatteredobjectandfoundtobeunstable
theprobabilityoffindingbychancetwoobjectswithsuchasmall withinthestandardparadigmover10Myrtime-scalesduetoNep-
angularseparationbetweentheirdirectionsofperiheliaand,whatis tuneperturbations.BothETNOsareratherunstablewithinsomein-
moreimportant,alsobetweentheirorbitalpolesislessthan0.0001, carnationsofthePlanetNinehypothesis(delaFuenteMarcos,de
whichsuggestsacommondynamicalorigin.However,aprobable laFuenteMarcos &Aarseth2016). Theheliocentric orbitsavail-
commondynamicalorigindoesnotimplyacommonphysicalori- able in 2016 August1,2 have been used to compute the values of
gin. In an attempt to unravel their physical nature, visible spec- theangularseparationsquotedintheprevioussection.Inspiteof
troscopyofthetwotargetswasobtainedon2016Septemberusing thelimitationsoftheorbitalsolutionof2013RF ,theuncertain-
98
the OSIRIS camera-spectrograph at the 10.4 m Gran Telescopio tiesmainlyaffectorbital elementsother thaninclination,i,longi-
Canarias (GTC) telescope, located in La Palma (Canary Islands, tudeoftheascendingnode,Ω,andargumentoftheperihelion,ω.
Spain).Here,wepresentanddiscusstheresultsoftheseobserva- These three orbital parameters are the only ones involved in the
tions. This Letter is organized as follows. Section 2 reviews the calculationofthedirectionsofperihelia,locationoforbitalpoles,
state of the art for this pair of ETNOs. The new observations — and directionsof velocitiesat perihelion (de laFuenteMarcos &
includingspectroscopy,photometryandastrometry—andtheirre- de la Fuente Marcos 2016). In sharp contrast, the value of Q of
sultsarepresentedinSection3.Thepossibleoriginofthispairis 2013RF isaffectedbyasignificantuncertainty(12percent).
98
exploredinSection4,makinguseofthenewobservationalresults
andN-bodysimulations.ConclusionsaresummarizedinSection5.
3 OBSERVATIONS
3.1 Spectroscopy
2 THEPAIR474640–2013RF :STATEOFTHEART
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Visible spectra of the two targets were obtained using OSIRIS
Asteroid (474640) 2004 VN112 was discovered on 2004 Novem- (Cepaetal.2000)at10.4mGTC.Theapparentvisualmagnitude,
ber6bytheESSENCEsupernovasurveyobservingwiththe4m V, at the time of observation was 23.3 for (474640) 2004 VN
112
Blanco Telescope from Cerro Tololo International Observatory (heliocentric distance of 47.7 au and phase of 1◦.1) and 24.4 for
(CTIO)at an apparent magnitude R of 22.7 (Becker et al.2007). 2013RF (36.6au,1◦.3).Foreachtarget,acquisitionimagesinthe
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Its absolute magnitude, H = 6.4 (assuming a slope parameter, G Sloan r′ filter were obtained in separate nights in order to iden-
= 0.15), suggests a diameter in therange 130–300 km for an as- tifyreliably theobject inthefieldof view. Thisprocedure ended
sumed albedo in the range 0.25–0.05. The orbital solution (2016 upbeingthemostefficienttodetect thesedim,slow-moving(ap-
August)forthisobjectisbasedon31observationsspanningadata- parentpropermotion<2′′/h)targets.Visiblespectrawereacquired
arcof5113dor14yr,from2000September26to2014September usingthelow-resolutionR300Rgrism(resolutionof348measured
26,itsresidualrmsamountsto0′.′19.1 Suchanobjectwouldhave atacentralwavelengthof6635Åfora0′.′6slitwidth),thatcovers
been visible to ESSENCE for only about 2 per cent of its orbit, thewavelengthrangefrom0.49to0.92µm,anda2′′slitwidth.Two
suggesting that the size of the population of minor bodies mov- widelyacceptedsolaranaloguestarsfromLandolt(1992)—SA93-
ing in orbits similar to that of 474640 could be very significant 101andSA115-271—wereobservedusingthesamespectralcon-
(Beckeretal.2008).Sheppard(2010)givesanormalisedspectral figurationatanairmassidenticaltothatofthetargetstoobtainthe
gradient of 11±4 %/0.1 µm for this object based on Sloan g′, r′, reflectancespectraoftheETNOs.ForagivenETNO,thespectrum
i′opticalphotometryacquiredin2008.Someadditionalphotome- wasthendividedbythecorrespondingspectrumofthesolarana-
trywasobtainedwiththeHubbleWideFieldCamera3(Fraser& log.AdditionaldatareductiondetailsaredescribedbydeLeónet
Brown2012).Itsopticalcoloursarerelativelyneutralandthiswas al.(2016) andMorateet al.(2016). For474640 weacquired two
interpretedbyBrown(2012) asasignthatitisnot dominatedby spectraof1800seach,whilefor2013RF weacquiredfourin-
98
methaneirradiationproducts. dividual spectra of 1800 s each. Observational details are shown
Asteroid2013RF98wasdiscoveredon2013September12by inTable1.Theresultingindividualreflectancespectra,normalised
theDarkEnergyCamera(DECam,Flaugheretal.2015)observing to unity at 0.55 µm and offset vertically for clarity, are shown in
fromCTIOfortheDarkEnergySurvey(DES,Abbottetal.2005) Fig.1.
atanapparentmagnitudezof23.5(Abbottetal.2016).Itsabsolute InTable1,thespectralslope(inunitsof%/0.1µm)hasbeen
magnitude, H =8.7,suggestsadiameterintherange50–120km. computed from a linear fittingto the spectrum in the wavelength
Theorbitalsolution(2016August)forthisETNOisratherpooras range0.5–0.9µm.Weusedaniterativeprocess—removingatotal
itisbasedon38observationsspanningadata-arcofjust56d,from of50pointsrandomlydistributedinthespectrumandperforminga
2013September12to2013November7,itsresidualrmsamounts linearfitting—andobtainedavalueoftheslopeforeachiteration.
The resulting slope value is the mean of a total of 100 iterations
1 OrbitavailablefromJPL’sSmall-BodyDatabaseandHorizonsOn-Line
EphemerisSystem:a =318±1au,e = 0.8513±0.0005,i = 25◦.5748± 2 Orbit available from Horizons:a = 307±37au,e = 0.882±0.015,
0◦.0004,Ω=65◦.9990±0◦.0007andω=327◦.121±0◦.010,referredtothe i = 29◦.62±0◦.08,Ω = 67◦.51±0◦.13andω = 316◦±6◦,referredtothe
epoch2457600.5JDTDB. epoch2457600.5JDTDB.
MNRAS000,1–6(2017)
Visiblespectraof(474640)2004 VN –2013RF 3
112 98
3.5 3.0
(474640) 2004 VN
112 (474640) 2004 VN
e 3.0 e 2.5 112
c c
n n
ecta 2.5 Spec#1 ecta 2.0
efl 2.0 efl
R R
ve 1.5 ve 1.5 2013 RF
elati 1.0 elati 1.0 98
R Spec#2 R
0.5 0.5
0.0 0.0
8 0.4 0.5 0.6 0.7 0.8 0.9 1.0
2013 RF98 Wavelength (µm)
e
c
an 6 Spec#1
ct Figure2.FinalvisiblespectraofthepairofETNOs(seethetextfordetails).
e
Refl 4 Spec#2
e
v
elati 2 Spec#3 2 (474640) 2020041 3V RNF19182
R 1.8
Spec#4 nce
0 0.4 0.5 W0.a6velen0g.t7h (µm0).8 0.9 1.0 Relative Reflecta 111 ...1246
Figure1.Individual visible spectra of(474640) 2004VN112 (toppanel) 0.8
and2013RF98 (bottompanel)normalisedtounityat0.55µmandoffset 0.6
verticallyforclarity.Redlinescorrespondtothelinearfittingintherange 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
Wavelength (µm)
0.5–0.9µmtocomputethespectralslope.
Figure3.Comparison between thespectra of(474640)2004VN112 and
2013RF98smoothedbyaSavitzky-Golayfilter(seethetext)andscaledto
Table1.Observationaldetailsofthevisiblespectra(1800seach)obtained matchat0.60µm.Themostprominentabsorptionbandofpuremethaneice
for(474640)2004VN112and2013RF98(seethetextforfurtherdetails). at0.73µmisnotseenoneitherspectra.
Target Spec# Date UTStart Airmass Slope(%/0.1µm)
1 09-03-16 04:37 1.085 10.2±0.6 ativereflectanceisbothslowly varying andcorrupted by random
noise,weappliedaSavitzky-Golayfilter(Savitzky&Golay1964)
474640 2 09-03-16 05:07 1.072 13.3±0.6
tobothdatasets.Suchfiltersprovidesmoothingwithoutlossofres-
Mean 12±2
olution,approximatingtheunderlyingfunctionbyapolynomialas
1 09-08-16 03:07 1.234 14.9±0.8 described by e.g. Press et al. (1992). Fig. 3 shows the smoothed
2 09-08-16 03:37 1.181 12.3±0.8 spectra after applying a65 point Savitzky-Golay filter of order 6
2013RF98 3 09-08-16 04:07 1.151 17.1±0.8 to the data in Fig. 2. The smoothed spectra, in particular that of
4 09-08-16 04:38 1.142 16.1±0.8 474640(blue),showsomeweakfeaturesthatmightbetentatively
Mean 15±2 identifiedaspuremethaneiceabsorptionbands(Grundy,Schmitt
& Quirico 2002). However, the most prominent methane band at
0.73µmisobservedneitherinthespectrumof474640norinthat
andtheassociatederroristhestandarddeviationofthismean.The of2013RF (red).TheS/Nisinsufficienttoidentifyreliablyany
98
process of dividing by the spectra of the solar analogue stars in- absorptionband, butthespectralslopesinthevisibleof bothob-
troduces an error of 0.3 %/0.1 µm. The error value shown in the jectsprovidesomecompositionalinformation.Objectswithvisible
lastcolumnofTable1issumofthesetwocontributions.Foreach spectralslopesintherange0–10%/0.1µmcanhavepureiceson
target, we averaged individual spectra to obtain the average visi- their surfaces (like Eris, Pluto, Makemake and Haumea), as well
blespectrafor 474640 and 2013 RF showninFig.2; themean as highly processed carbon. Slightlyred slopes (5–15 %/0.1 µm)
98
spectral slopes inTable1arethe meansof theindividual spectra indicatethepossiblepresenceofamorphoussilicatesasinthecase
and their errors, the associated standard deviations. The value of ofTrojans(Emery&Brown2004)orThereus(Licandro&Pinilla-
thespectralslopeof474640isconsistentwiththeoneobtainedby Alonso2005).Inanycase,theobjectswillnothaveasurfacedomi-
Sheppard(2010).ThevaluesinTable1aresimilartothoseofscat- natedbycomplexorganics(tholins).Differencesbetweenthespec-
tereddiscTNOs,Plutinos,high-inclinationclassicalTNOsaswell traof474640and2013RF mightbetheresultoftheirpresent-day
98
astheDamocloidsandcomets(seee.g.table5inSheppard2010). heliocentricdistance.Mechanismsthataremoreefficientinalter-
The spectra in Fig. 2 show an obvious resemblance, but the ingtheicysurfacesoftheseobjectsatsmallerperiheliondistances
low S/N makes the identification of absorption features difficult. includesublimationofvolatilesandmicrometeoroidbombardment
In order to make a better comparison and assuming that the rel- (Santos-Sanzetal.2009).
MNRAS000,1–6(2017)
4 J. deLeón, C. delaFuenteMarcos andR. delaFuenteMarcos
3.2 Photometry 4.5
4
W(47e4o6b4t0a)in2e0d04a VtoNtal ofan3da2n0d1311RFacq,uriseistpioenctiivmelayg.eIsmtaogeidsewnteifrye on () 3.5
112 98 o 3
mtvaakaluegnensiutuscdionemgspatuhntededSthlefooiarrnutnrh′ceefirclttaoeirrnretaisnepsdoancrdaeilnisbhgroawnteingdhiuntss.TinaTgbhlteehAere1zse.urlotinpgoinr′t ular separati 12 ..255
g
n 1
A
0.5
3.3 Astrometry 0
-10 -8 -6 -4 -2 0
Time (Myr)
Weusedtheacquisitionimagestocomputethecelestialcoordinates
ofeachtargetandimproveitsorbit.Thiswasparticularlyrelevant Figure4.Evolutionoftheangularseparationbetweentheorbitalpolesof
for2013RF98thatpriortoourobservationshadaratheruncertain thepair(474640)2004VN112–2013RF98forthreerepresentativetestcal-
orbitaldetermination.2Wefound(474640)2004VN within1′′of culationswithdifferentperturbers.Red:a=549au,e=0.21,i=47◦,m=
the predicted ephemerides, but 2013 RF was fou1n12d nearly 1.′2 16M⊕.Blue:a=448au,e=0.16,i=33◦,m=12M⊕.Green:a=421au,
away. BothETNOswerein Cetus. Astro9m8etriccalibration of the e=0.10,i=33◦,m=12M⊕.
CCD frames was performed using the algorithms of the Astrom-
etry.net system (Lang et al. 2010). The quality of high-precision
astrometrywithOSIRISatGTCmatchesthatofdataacquiredwith brokeuprelativelyrecentlyatperihelionandthesetwoETNOsare
FORS2/VLT (Sahlmann et al. 2016). The collected astrometry is fragments,or(2)bothETNOswerekickedbyanunseenperturber
showninTablesA2andA3.Theneworbitalsolutionfor2013RF98 ataphelion.Sekanina(2001)hasshownthatminorbodiesresulting
availablefromHorizons(asof2016December1818:51:59UT)is fromafragmentationepisodeatperihelionmusthaveverydiffer-
basedon51observationsspanningadata-arcof1092d,itsresid- enttimesofperihelionpassage.Thefragmentationepisodeatper-
ual rms amounts to 0′.′12: a = 349±11 au, e = 0.897±0.003, ihelion can thus be readily discarded as the difference in time of
i = 29◦.572±0◦.003, Ω = 67◦.596±0◦.005 and ω = 311◦.8±0◦.6, perihelionpassageforthispairislessthanayear.
referred to the epoch 2457800.5 JD TDB; the time of perihelion The second scenario pointed out above impliesthe presence
passageis2455125±95JED(2009October20.7289UT).Thetime ofanunseenmassiveperturber,i.e.atrans-Plutonianplanet.Close
ofperihelionpassagefor474640is2009August25.8290UT.Us- encountersbetweenminorbodiesandplanetscaninducefragmen-
ing the new orbit, the directions of the perihelia of this pair are tationdirectlyviatidalforces(e.g.Sharma,Jenkins&Burns2006)
separatedby14◦.2±0◦.6,theirorbitalpolesby4◦.056±0◦.003,andthe or indirectlyby excitingrapidrotation (e.g.Scheeres et al.2000;
directionsoftheirvelocitiesatperihelion/aphelionby14◦.1±0◦.6. Ortizetal.2012).Alternatively,widebinaryasteroidscanbeeas-
ilydisrupted during close encounters with planets. The existence
of wide binaries among the populations of minor bodies orbiting
beyondNeptuneiswelldocumented(e.g.Parkeretal.2011).Wide
4 ORIGINOFTHEPAIR474640–2013RF :
98 binary asteroids have very low binding energies and can be eas-
FRAGMENTATIONVS.BINARYDISSOCIATION
ilydissociatedduringcloseencounterswithplanets(e.g.Agnor&
Fromthespectralanalysisdiscussedabove,wehavefoundthatthe Hamilton2006;Parker&Kavelaars2010).Binaryasteroiddisso-
membersofthepair(474640)2004VN –2013RF showsimilar ciationmaybeabletoexplainthepropertiesofthispairofETNOs,
112 98
spectralslopes,verydifferentfromthatofSednawhichhasultra- butonlyifthereisamassiveunseenperturberorbitingtheSunwell
red surface material (spectral gradient of about 26 %/0.1 µm ac- beyondPluto.
cordingtoSheppard2010,and42%/0.1µmaccordingtoFornasier Inorder totest theviabilityofthishypothesis, wehaveper-
et al. 2009) but compatible with those of (148209) 2000 CR formedthousandsofnumericalexperimentsfollowingtheprescrip-
105
(spectral gradient of about 14 %/0.1 µm, Sheppard 2010) and tionsdiscussedbydelaFuenteMarcosetal.(2016)andaimedat
2012 VN (spectral gradient of about 13 %/0.1 µm, Trujillo & findingthemostprobableorbitalpropertiesofaputativeperturber
113
Sheppard2014).Thesefiveobjectshavebeenincludedinthegroup abletotilttheorbitalplaneofthepair474640–2013RF froman
98
of seven singled out as relevant to the Planet Nine hypothesis initial angular separation close to zero at dissociation to the cur-
(Brown & Batygin 2016). Such spectral differences suggest that rentvalueofnearly4◦.ThesesimulationsinvolveN-bodyintegra-
the region of origin of the pair 474640–2013 RF may coincide tionsbackwardsintimeundertheinfluenceofanunseenperturber
98
withthatof148209and2012VN butnotwithSedna’s,whichis withvaryingorbitalandphysicalparameters(pernumericalexper-
113
thoughttocomefromtheinnerOortCloud(Sheppard2010).Other iment).Ourpreliminaryresultsindicatethataplanetwithmass,m,
ETNOswithvalues of their spectral gradient inSheppard (2010) in the range 10–20 M moving in an eccentric (0.1–0.4) and in-
⊕
are2002GB (∼17%/0.1µm)and2003HB (∼13%/0.1µm). clined(20–50◦)orbitwithsemimajoraxisof300–600au,maybe
32 57
Objects with both similar directions of the orbital poles and abletoinducetheobservedtiltonatime-scaleof5–10Myr.Per-
periheliacouldbepartofagroupofcommonphysicalorigin(Öpik turberswithm < 10 M ora > 600auareunabletoproducethe
⊕
1971).ThisparticularpairofETNOsisveryunusualandamodel desired effect. Fig. 4 illustrates the typical outcome of these cal-
analogoustotheoneusedbydelaFuenteMarcos&delaFuente culations.Adetailedaccountofthesenumericalexperimentswill
Marcos(2014)tostudytheoverallvisibilityoftheETNOpopula- bepresented inanaccompanying paper (delaFuenteMarcos, de
tionpredictsthattheprobabilityoffindingsuchapairbychance la Fuente Marcos & Aarseth, in preparation). The orbital param-
islessthan0.0002.Thismodelusestheneworbitalsolutionsand etersofthisputativeplanetaresomewhatconsistentwiththoseof
assumesanunperturbedasteroidpopulationmovinginheliocentric theobjectdiscussedbyHolman&Payne(2016).Super-Earthsmay
orbits. FollowingÖpik (1971), thereare twoindependent scenar- format125–750aufromtheSun(Kenyon&Bromley2015,2016).
iosthat couldexplainthislevelof coincidence: (1)alargeobject Ouranalysisfavoursascenarioinwhich474640–2013 RF were
98
MNRAS000,1–6(2017)
Visiblespectraof(474640)2004 VN –2013RF 5
112 98
onceabinaryasteroidthatbecameunboundafterarelativelyrecent REFERENCES
gravitationalencounterwithatrans-Plutonianplanetathundredsof
Abbott T. et al., 2005, The Dark Energy Survey, eprint arXiv:astro-
aufromtheSun.Analternativeexplanationinvolvinganasteroid
ph/0510346
break-upnearaphelion,alsoafteracloseencounterwithaplanet,is
AbbottT.etal.,2016,MNRAS,460,1270
possiblebutlessprobablebecauseitrequiresanapproachatcloser AgnorC.B.,HamiltonD.P.,2006,Nature,441,192
range,20planetaryradiiversus0.8auforbinarydissociation. BatyginK.,BrownM.E.,2016,AJ,151,22
BeckerA.C.,ArrakiK.S.,RestA.,Wood-VaseyW.M.,MarsdenB.G.,
2007,MPECCirc.,MPEC2007-S29
BeckerA.C.etal.,2008,ApJ,682,L53
BrownM.E.,2012,Annu.Rev.EarthPlanet.Sci.,40,467
BrownM.E.,BatyginK.,2016,ApJ,824,L23
5 CONCLUSIONS
CepaJ.etal.,2000,inIyeM.,MoorwoodA.F.M.,eds,OpticalandIR
In this Letter, we provide for the first time direct indication of TelescopeInstrumentationandDetectors.Proc.SPIE,4008,p.623
thesurfacecomposition oftheETNOs(474640) 2004 VN and delaFuenteMarcosC.,delaFuenteMarcosR.,2014,MNRAS,443,L59
112
delaFuenteMarcosC.,delaFuenteMarcosR.,2016,MNRAS,462,1972
2013 RF . Both objects are too faint for infrared spectroscopy,
98 delaFuenteMarcosC.,delaFuenteMarcosR.,AarsethS.J.,2015,MN-
but our results show that they are viable targets for visible spec-
RAS,446,1867
troscopy. The analysis of our results gives further support to the
delaFuenteMarcosC.,delaFuenteMarcosR.,AarsethS.J.,2016,MN-
trans-Plutonianplanetsparadigmthatpredictsthepresenceofone
RAS,460,L123
ormoreplanetarybodieswellbeyondPluto.Summarizing: deLeónJ.etal.,2016,Icarus,266,57
deLeónJ.,delaFuenteMarcosC.,delaFuenteMarcosR.,2016,MPEC
(i) Our estimate of the spectral slope for 474640 is
Circ.,MPEC2016-U18
12±2%/0.1µmandfor2013RF98is15±2%/0.1µm.These EmeryJ.P.,BrownR.H.,2004,Icarus,170,131
valuessuggestthatthesurfacesoftheseETNOscanhavepure FlaugherB.etal.,2015,AJ,150,150
methane ices (like Pluto) and highly processed carbons, in- FornasierS.etal.,2009,A&A,508,457
cludingsomeamorphoussilicates. FraserW.C.,BrownM.E.,2012,ApJ,749,33
(ii) Althoughthespectraofthepair474640–2013RF arenot GladmanB.,HolmanM.,GravT.,KavelaarsJ.,NicholsonP.,AksnesK.,
98
PetitJ.-M.,2002,Icarus,157,269
perfectmatches,theresemblanceissignificantandthedispar-
GrundyW.,SchmittB.,QuiricoE.,2002,Icarus,144,486
itiesobservedmightbetheresultoftheirdifferentpresent-day
HolmanM.J.,PayneM.J.,2016,AJ,152,80
heliocentricdistance.
KenyonS.J.,BromleyB.C.,2015,ApJ,806,42
(iii) Byimprovingtheorbitalsolutionof2013RF ,weconfirm
98 KenyonS.J.,BromleyB.C.,2016,ApJ,825,33
thatthepair474640–2013RF98hasunusualrelativedynam- LandoltA.U.,1992,AJ,104,340
icalproperties.Thedirectionsoftheirperiheliaareseparated LangD.,HoggD.W.,MierleK.,BlantonM.,RoweisS.,2010,AJ,139,
by14◦.2andtheirorbitalpolesare4◦.1apart. 1782
(iv) Ournumericalanalysisfavoursascenarioinwhich474640– LicandroJ.,Pinilla-AlonsoN.,2005,ApJ,630,L93
2013RF wereonceabinaryasteroidthatbecameunbound MorateD.,deLeónJ.,DePráM.,LicandroJ.,Cabrera-LaversA.,Campins
98
afteranencounterwithatrans-Plutonianplanetatverylarge H.,Pinilla-AlonsoN.,Alí-LagoaV.,2016,A&A,586,A129
MorbidelliA.,LevisonH.F.,2004,AJ,128,2564
heliocentricdistance.
ÖpikE.J.,1971,IrishAstronomicalJournal,10,35
OrtizJ.L.etal.,2012,MNRAS,419,2315
ParkerA.H.,KavelaarsJ.J.,2010,ApJ,722,L204
ParkerA.H.,KavelaarsJ.J.,PetitJ.-M.,JonesL.,GladmanB.,ParkerJ.,
2011,ApJ,743,1
ACKNOWLEDGEMENTS PressW.H.,TeukolskyS.A.,VetterlingW.T.,FlanneryB.P.,1992,Nu-
mericalRecipesinFORTRAN.CambridgeUniv.Press,Cambridge,p.
We thank the anonymous referee for a constructive and detailed 644
report, and S. J. Aarseth for providing one of the codes used in SahlmannJ.,LazorenkoP.F.,BouyH.,MartínE.L.,QuelozD.,Ségransan
thisresearchandforhishelpfulcommentsonbinarydissociation. D.,ZapateroOsorioM.R.,2016,MNRAS,455,357
Based on observations made with the Gran Telescopio Canarias; Santos-SanzP.,OrtizJ.L.,Barrera L.,Boehnhardt H.,2009,A&A,494,
wearegratefultoallthetechnicalstaffandtelescopeoperatorsfor 693
theirassistancewiththeobservations.Thisworkwaspartiallysup- SavitzkyA.,GolayM.J.E.,1964,AnalyticalChemistry,36,1627
ScheeresD.J.,OstroS.J.,WernerR.A.,AsphaugE.,HudsonR.S.,2000,
portedbytheSpanish‘MinisteriodeEconomíayCompetitividad’
Icarus,147,106
(MINECO)under grantESP2014-54243-R.JdLacknowledges fi-
Sekanina Z., 2001, Publications of the Astronomical Institute of the
nancialsupportfromMINECOunderthe2015SeveroOchoaPro-
AcademyofSciencesoftheCzechRepublic,89,78
gram MINECO SEV-2015-0548. CdlFM and RdlFM thank A. I.
ShankmanC.,KavelaarsJ.J.,LawlerS.M.,GladmanB.J.,BannisterM.
GómezdeCastro,I.LizasoainandL.HernándezYáñezoftheUni- T.,2016,AJ,submitted(eprintarXiv:1610.04251)
versidad Complutense de Madrid (UCM) for providing access to SharmaI.,JenkinsJ.T.,BurnsJ.A.,2006,Icarus,183,312
computingfacilities.Partofthecalculationsandthedataanalysis SheppardS.S.,2010,AJ,139,1394
werecompletedontheEOLOclusteroftheUCM,andCdlFMand SheppardS.S.,TrujilloC.A.,2016,AJ,152,221
RdlFMthankS.CanoAlsúaforhishelpduringthisstage.EOLO, TrujilloC.A.,SheppardS.S.,2014,Nature,507,471
theHPCofClimateChangeoftheInternationalCampusofExcel-
lenceofMoncloa,isfundedbytheMECDandMICINN.Thisisa
contributiontotheCEIMoncloa.InpreparationofthisLetter,we
madeuseoftheNASAAstrophysicsDataSystem,theASTRO-PH
e-printserverandtheMPCdataserver.
MNRAS000,1–6(2017)
6 J. deLeón, C. delaFuenteMarcos andR. delaFuenteMarcos
TableA1.Observationaldetailsoftheacquisitionimagesobtainedtoiden- ThispaperhasbeentypesetfromaTEX/LATEXfilepreparedbytheauthor.
tifythetargets.
Image# Date UTStart Airmass Exp.Time Zeropoint r′
(s) (mag) (mag)
(474640)
2004VN112
1 09-02-16 02:16 1.580 120 29.240 23.63±0.10
2 09-03-16 04:21 1.120 120 29.277 23.58±0.05
3 09-03-16 04:32 1.100 60 29.277 23.51±0.05
2013RF98
1 09-05-16 02:43 1.380 180 29.281 24.57±0.10
2 09-06-16 02:55 1.320 120 29.287 24.39±0.20
3 09-06-16 03:05 1.290 120 29.287 24.42±0.15
4 09-06-16 03:23 1.240 120 29.287 24.51±0.20
5 09-06-16 03:32 1.220 120 29.287 24.45±0.05
6 09-06-16 03:37 1.210 120 29.287 24.53±0.20
7 09-07-16 03:40 1.210 180 29.287 24.53±0.05
8 09-08-16 02:46 1.330 120 29.287 24.56±0.07
9 09-08-16 02:51 1.310 180 29.287 24.55±0.10
10 09-08-16 02:56 1.290 120 29.287 24.53±0.05
11 09-08-16 03:00 1.280 120 29.287 24.49±0.10
TableA2.Observationsof(474640)2004VN112.Alltheobservations in
ther′filter.
Date RA(J2000) Dec(J2000)
(UT) (h:m:s) (◦:′:′′)
20160902.09514 03:07:52.51 +07:38:28.1
20160903.18233 03:07:51.41 +07:38:17.7
20160903.18923 03:07:51.40 +07:38:17.5
TableA3.Observationsof2013RF98.Alltheobservationsinther′filter.
Date RA(J2000) Dec(J2000)
(UT) (h:m:s) (◦:′:′′)
20160905.114385 02:49:09.83 −00:10:52.0
20160906.122606 02:49:07.83 −00:11:14.2
20160906.129458 02:49:07.81 −00:11:14.5
20160906.142113 02:49:07.79 −00:11:14.7
20160906.148191 02:49:07.78 −00:11:14.7
20160906.151823 02:49:07.77 −00:11:14.8
20160907.154454 02:49:05.70 −00:11:37.3
20160908.116547 02:49:03.61 −00:11:59.1
20160908.120114 02:49:03.60 −00:11:59.1
20160908.123483 02:49:03.60 −00:11:59.3
20160908.126326 02:49:03.59 −00:11:59.4
APPENDIXA: PHOTOMETRYANDASTROMETRY
DATATABLES
Ther′magnitudesfromtheacquisitionimagesandtheiruncertain-
tiesareshowninTableA1.TheastrometrysubmittedtotheMinor
PlanetCenter(MPC)isshowninTablesA2andA3(deLeón,dela
FuenteMarcos&delaFuenteMarcos2016).
MNRAS000,1–6(2017)